/Engine/Source/Editor/Kismet/Public/BlueprintCompilationManager.h
Returns the Default Value associated with ForClass::Property, if ForClass is currently being compiled this function can look at the old version of the CDO and read the default value from there
static bool GetDefaultValue ( const [UClass](API\Runtime\CoreUObject\UObject\UClass) * ForClass, const [FProperty](API\Runtime\CoreUObject\UObject\FProperty) * Property, [FString](API\Runtime\Core\Containers\FString) & OutDefaultValueAsString )